1. Field of the Invention
The present invention relates to a reinforced upper frame for supporting a cabin of heavy construction equipment using a welding deformation preventing structure and a method of manufacturing the same, and more particularly, to an upper frame of heavy construction equipment capable of preventing structural deformation of a machined center frame when a side frame is welded or fixed to the center frame.
2. Description of the Prior Art
FIG. 1 is a cross-sectional view illustrating the construction of a cabin mounted on a conventional upper frame, and FIG. 2 is a perspective view illustrating the construction of a conventional upper frame.
Referring to FIG. 1, heavy construction equipment, such as an excavator, generally includes an upper frame 2 that can be rotated above and is mounted on a lower driving structure (not shown), a cabin 4 mounted on the upper frame 2, and vibration absorption devices 8 and 10, installed between the upper frame 2 and the base plate of the cabin 4, for resiliently supporting the cabin 4 with respect to the upper frame 2 and connecting the base plate to the upper frame 2, with the base plate being spaced apart from the upper frame 2 at a constant interval.
Referring to FIG. 2, the upper frame 2 has a center frame 20, on which an operation device is mounted, and left and right frames 30 and 40 each mounted on left and right sides of the center frames 20. The center frame 20 has lower plates 22, on which a swing ring gear is mounted, and lateral plates 24 vertically mounted on the lower plates 22 and connected to the operation device. The left and right frames 30 and 40 have a side channel 32 extended in a longitudinal direction and a plurality of side frames 34 connecting the center frame 20 with the side channel 32.
The vibration absorption devices 8 and 10 that support the cabin 4 and absorb the shock applied from the exterior are mounted only on the left frame 30; therefore, only the left frame 30 is provided with a plurality of through-holes 36 through which the vibration absorption devices 8 and 10 are mounted. Here, the side frame 34 mounted on the left frame 30 will now be described.
In order to connect the left frame 30 to the center frame 20, the left frame 30 is simultaneously welded to the lower plate 22 and the lateral plate 24 of the center frame 20. That is, in order to obtain welding strength, each end of a plurality of the side frames 34 is welded to the lower plate 22 of the center frame 20, on which the swing ring gear is mounted, and the lateral plate 24 of the center frame 20, on which the operation device is mounted.
If the left frame 30 is directly welded to the lower plate 22 of the center frame 20, on which the swing ring gear is mounted, the portion, in which the swing ring gear is fastened to the lower plate 22, is subjected to thermal deformation due to welding. Consequently, flatness of the lower plate 22 closely fastened to the swing ring gear is adversely affected, which may shorten a life span of the swing ring gear. Furthermore, another problem is that the vertical rocking of an upper swing structure causes the precision of the operation to deteriorate.
The contact portion A between the lower plate 22 of the center frame 20 and the side frame 34 of the left frame 30 is not welded to avoid thermal deformation that results from welding; but only the contact portion B between the lateral plate 24 of the center frame 20 and the side frame 34 of the left frame 30 is welded.
When the heavy construction equipment rolls over or is applied with excessive shock from the exterior, the stress is concentrated upon the welded portion, i.e., the vertical contact portion between the lateral plate 24 of the center frame 20 and the side frame 34 since the horizontal contact portion between the lower plate 22 of the center frame 20 and the side frame 34 is not welded, and thus the welded portion is easily broken, e.g., by creation of cracks. Therefore, its strength and durability are limited.